The present invention relates to the use of water-soluble or water-swellable copolymers based on acrylamidoalkylsulfonic acid salts as drift control agents in crop protection compositions.
Pesticides are applied in a highly efficient manner to agricultural production fields using spray tanks in airplanes, tractors and other devices. To achieve an application of the active substances which is as accurate as possible, it is necessary to obtain a spray cone which is as narrow as possible, and to avoid a drift of the spray mist from the target area.
The drift of the spray cone is determined substantially by the droplet size. The smaller the droplets, the longer the residence time in the air and the higher the tendency to evaporate and/or to drift horizontally and to miss the target location. The drift effect can be reduced considerably by adding suitable drift control agents to pesticide formulations, which drift control agents increase the size of the droplets in the spray mist. The formulations modified by drift control agents additionally have to be insensitive to shear forces to which they are exposed in the spray pumps and nozzles. Drift control agents are furthermore required to have good biological degradability, compatibility with the other components of the crop protection composition and high storage and temperature stability. It is well known in the prior art that the rheological properties of aqueous compositions can be modified by adding water-soluble polymers, for example polyacrylamides, acrylamide/acrylic acid polymers, sodium polyacrylate, carboxymethylcellulose, hydroxyethylcellulose, methylcellulose, polysaccharides and natural and synthetic guar gum
(U.S. Pat. Nos. 4,413,087, 4,505,827, 5,874,096).
Unsatisfactory is the viscoelastic behavior of the additives when shear and pressure forces are applied.
Under mechanical stress in the spraying device, the viscosity is lowered and the droplet size in the spray mist is reduced.
It is a further disadvantage that the polymers used for modifying the viscosity of the aqueous preparations lose some of their thickening action in the presence of electrolytes, for example sodium chloride, calcium chloride and magnesium sulfate. Cellulose derivatives are highly electrolyte-tolerant but not temperature-stable enough. Biopolymers, such as xanthan gum, are electrolyte- and thermostable, but expensive and poorly storage-stable.
Both for economical and ecological reasons, there are attempts to find suitable drift control agents which effectively increase the droplet volumes of the aqueous compositions, even under the influence of shear forces, in the presence of electrolytes and under thermal stress, and which reduce the drift of the spray cone.
Polymers of acrylamido-2-methyl-propanesulfonic acid and acrylamide and their use as additives in cement slurries for cementing deep underground drillings are known from DE 197 52 093.
Surprisingly, it has been found that water-soluble and water-swellable copolymers based on acrylamidoalkylsulfonates and olefinically unsaturated monomers containing at least one oxygen, nitrogen, sulfur or phosphorus atom and from 0 to 20% by weight of a suitable crosslinker are very good thickeners for aqueous preparations and, when these compositions are sprayed, effect an increase in the particle size and a reduction of the spray cone. In addition, the polymers used according to the invention have good viscosity properties. Under the action of shear forces, the particle volumes are reduced only slightly. In addition, the compositions according to the invention have high electrolyte, temperature and storage stability.